This dino had a nine-inch-thick skull.

A dino with a dome-shaped head grazes on ferns along a shoreline in what’s now Wyoming about 70 million years ago. Suddenly, another of its kind—called Pachycelphalosaurus—approaches, hungry for some greenery, too. The two aren’t willing to share, so they ram their nine-inch-thick skulls into each other’s bodies. Whichever dino backs down first will have to leave.

Tough skull

Pachycelphalosaurus’s skull was about 20 times thicker than most other dinosaur noggins, so its name makes sense—it means “thick-headed lizard.” This nine-foot-long dino also had short, spiky horns surrounding the dome and extending down to its nose. But that might not how this dinosaur always looked. According to recent research, youngsters might’ve had had spikier skulls and no dome at all. (The skulls look so different that some scientists think these dinos are a different species altogether: Dracorex.) 

Like today’s bighorn sheep, this animal is often shown butting heads with its rivals. But scientists now think that Pachycephalosaurus wouldn’t have survived head-to-head combat. Instead, they think that these dinosaurs might have used their domes to whack each other on their sides to compete for territory or mates. The cool craniums might have also impressed a potential mate.

Go nuts

This plant-eater had some special teeth. Although it had typical leaf-eating teeth tucked behind its short beak, Pachycelphalosaurus had other teeth in its cheeks. That might have helped it grind up things like nuts and fruit.

Pachycephalosaurus walked alongside Triceratops, Ankylosaurus, and Tyrannosaurus rex in what’s now western North America during the Cretaceous period, but all of these animals went extinct when an asteroid hit Earth 66 million years ago.


Ali and Sean travel back 150 million years to the Jurassic period to get a look at a flying dinosaur called the Anchiornis. Tour guide Simon reveals that this dinosaur actually had feathers!